F9 and hemophilia B: In this study, we focused on exonic mutations in FIX gene that have been found in Hemophilia B patients, and particularly on exon 5 that encodes for EGF2 domain, which is crucial for the coagulant activity in the intrinsic coagulation pathway.[20] This exon contains several missense, nonsense and synonymous mutations,[21] whose potential effect on pre mRNA splicing has not been studied so far.